In a still camera, the importance of achieving accurate metering and registration of each image frame with the exposure gate in the frame-to-frame advance between exposures of a filmstrip has long been recognized. Proper frame alignment with the picture-taking optical axis not only ensures correct frame-to-frame spacing and avoidance of overlap in a series of exposed images, but also positions the film frame for properly locating exposure data and the like relating to a specific frame and recorded adjacent thereto on the film at the time of exposure for later reference in producing prints. Harvey U.S. Pat. No. 4,639,111, for example, discloses marginal encoding by optical means adjacent a frame at the time of exposure of frame specific field of view identification information in a tele/pan camera.
Cameras incorporating drive mechanisms for the frame-to-frame film transport between supply and take-up reels have means for stopping the advance of film along a camera exposure plane, at a position of registration of the next available frame in optical alignment with a picture-taking optical axis. A common practice of achieving accuracy of metering and registration is to utilize film resident, frame correlated marginal fiducials in the form of single perforations per frame, which can be detected to determine the correct positioning for the next frame.
A well-known conventional system, uses a single perforation per frame film and a mechanical claw or pawl that detects the perforation corresponding to the next frame and establishes registration of that frame when that perforation reaches a desired stopping point. Examples of such film metering devices are shown in Beach U.S. Pat. Nos. 3,709,128 and 3,712,200; and Monks U.S. Pat. No. 3,724,348, the disclosures of which are incorporated herein.
Once registration is achieved, it is desirable to provide means to maintain such registration until commencement of the next exposure. In the absence of such provision, the film is subject to creep out of alignment due to vibration or physical shock forces exerted on the camera body or residual torque forces exerted by the drive mechanism. For cameras designed to operate with a single perforation per frame film, such as 110 and 126 format cameras, registration is typically maintained by engaging the pawl at a stopping point through the perforation and into a slot located in the camera wall or film cartridge, until the next exposure. The metering mechanism is usually mechanically coupled with the shutter release mechanism, to release the pawl from its registration engagement by a separate mechanical member which moves in response to taking the exposure. Because of the nature of the 110 and 126 film cartridges, the metering systems utilized therewith permit only a single frame-by-frame advance. Moreover, film motion is in a single direction only, with no rewind or prewind capability.
It is a desirable objective to have a film metering system that includes the positive mechanical engagement of a pawl tooth through a film perforation in order to maintain correct positional alignment of a filmstrip frame relative to an exposure gate, yet which is also suitable for use in cameras having a motorized film advance. It is also desirable to provide a mechanical pawl metering system that does not require mechanical interconnections with the shutter release mechanism. Another desirable objective is to have a film metering system that permits the film to be advanced by multiple frames at one time, if desired, and also allows the film to be prewound or rewound by being transported in a direction opposite to the normal frame-to-frame advance between exposures.
A film metering mechanism achieving those objectives is described in commonly-owned, copending U.S. patent application Ser. No. 486,489, entitled "Film Metering Apparatus and Method" and filed on even date herewith, the disclosure of which is incorporated herein by reference. An embodiment of metering mechanism described therein is suitable for use in motor drive film advance cameras using a single perforation per frame film metering fiducial to locate each film exposure frame in alignment with the camera exposure gate. That mechanism allows the film to be stopped in the proper registration position for each exposure, and maintains registration alignment by preventing further unintentional film motion through force balancing, once the film has been positioned. It also allows the film to be transported in either direction without stopping at perforations, if desired, and senses the passage of each perforation in either direction so that a frame count can be established.